Late blight

Late blight, caused by the oomycete Phytophthora infestans, is one of the most devastating plant diseases in global agriculture. While it is infamous for its impact on potatoes and tomatoes, it also affects a diverse range of crops including bulb onion, garlic, celery, asparagus, fodder beet, oilseed rape, and ornamental plants like Anemone coronaria (Slipper Flower). The pathogen thrives in cool, humid environments.

The first symptoms typically appear as water-soaked lesions on the leaves, which soon turn brown or black. Under high humidity, a whitish mold develops on the undersides of the leaves, consisting of sporangiophores. The disease spreads rapidly to stems and fruit. In tubers, it causes dark, sunken lesions and internal reddish-brown necrosis, which often leads to secondary infections and rapid decomposition of the entire harvest.

Conditions for development are strictly linked to moisture and temperature. High humidity, frequent rainfall, and temperatures between 15°C and 20°C create an environment where the fungus produces sporangia that can be spread by wind or water splashing. Phytophthora infestans survives between seasons primarily in infected tubers or plant debris left in the field, making sanitation a critical management factor.

The destructiveness of the disease is extreme, as it can cause complete crop loss within two weeks under favorable weather conditions. The damage is not limited to the growing season; infected tubers can rot in storage, impacting the marketability of the entire crop. Because the pathogen can produce new genetic variants (mating types), it is constantly evolving to overcome plant resistance.

Effective control requires a multi-faceted approach involving cultural practices and chemical interventions. Regular field scouting and the use of decision support systems can help time fungicide applications effectively. Key management strategies include:

• Planting certified disease-free seeds and tubers.
• Implementing wide crop rotations to break the disease cycle.
• Removing and destroying all cull piles and infected volunteer plants.
• Applying fungicides during periods of high humidity and risk.
• Selecting resistant varieties to reduce the overall disease pressure.